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Brinell Hardness Testing

The Brinell hardness test method, as defined in ASTM E10, test the samples whose structure or surface is either coarse or rough including forgings and castings. It has a high-test load (3000 kgf) and a 10mm diameter indenter, where the resultant indentation averages out the surface and sub-surface irregularities.

The Brinell method employs a predetermined test load (F) into a carbide ball of fixed diameter (D) held for a fixed time period and removed. The resultant impression can be measured using a customized Brinell microscope or optical system across a minimum of two diameters at right angles to each other after which these results are averaged (d). Though the calculation mentioned below can derive the Brinell number, a chart is used to convert the averaged diameter to a Brinell hardness number.

The test forces used for non-ferrous materials range from 500kgf up to 3000kgf for cast iron and steels. There are varied other Brinell scales where the load is as low as 1kgf with the indenter diameter of 1mm diameter, but they are infrequently used.

 

Brinell Hardness Testing
Brinell Hardness Testing

Test Method Illustration 

D = Ball diameter 

d = impression diameter 

L = load 

 

Usually, the key cause of error in Brinell testing is the determination of the indentation. Due to inconsistencies among the operators, while calculating the measurements, the final outcomes may vary even under the best ideal conditions. In the case of less than ideal conditions, it may lead to an increase in significant variation. The test surface is repeatedly prepared with the help of a grinder to eliminate surface conditions.

The pointed edge in this method makes it hard to interpret the indentation. Furthermore, when operators are well aware of all the specification limits for rejects, they can be inclined to figure out the measurements in a way that can extrapolate the percentage of ‘good’ tests with the least number of re-testing. 

There are two categories of technological remedies to sort out the Brinell measurement error issues, which have been established over the years. Automatic optical Brinell scopes, including the B.O.S.S. system, employ computers along with the image analysis to check the indentations in a persistent manner. This standardization helps in removing the operator subjectivity, thereby these operators will stay less prone to see in-tolerance results automatically in case if the sample’s result goes out-of-tolerance. 

Brinell units work by abiding by the ASTM E103 standards while measuring the samples using Brinell hardness parameters in addition to the Rockwell hardness method. This method delivers the most repeated results at a greater speed as the notions of optical interpretations are completely eliminated with the help of automatic mechanical depth measurement.

However, in this testing method, the outcomes may not be strictly consistent with Brinell’s results due to the implementation of varied test methods – a counterbalance to all the outcomes may be required for some materials in this case. It will be easier to show the right values in cases where this point arises as an issue. For more information about Brinell hardness tester, contact us.

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